He was arrested in Luuka distrct, east of the country, at the venue of a rally according to tweets posted by his aides.
The Daily Monitor newspaper reports that he was scheduled to address his supporters in the area.
Police accused him of violating COVID-19 safety measures on public gatherings as directed by the electoral commission, the newspaper added.
Ugandans will vote in a general election on 14 January to elect a president and members of parliament.
--BBC--